This implements a solution that preemptively exits the tick loop if we have already marked the connection as disconnecting. This avoids changing the result of Connection#isConnected in order to avoid other possibly unintentional changes. Fundamentally it should be investigated if closing the connection async is really still needed.
This also additionally removes the login disconnecting logic for server stopping, as this was also a possible issue in the config stage but also shouldn't be an issue as connections are closed on server stop very early.
Additionally, do not check for isConnecting() on VERIFYING, as that seemed to be an old diff originally trying to resolve this code, however isConnected is not updated at this point so it pretty much was useless.
Send more keepalives, record all transactions within the last minute.
We send more keepalives so that the latency calculation is more
accurate. Since we send more keepalives, we track all pending
keepalives in case multiple end up in flight.
Additionally, replace the latency calculation with a true
average over the last 5 seconds of keepalive transactions.
